The present invention relates to a control circuit for controlling the timing of driving a plurality of wire pins provided for a printing head of a serial impact printer, and more specifically to a control circuit for driving the wire pins of the printing head provided with inclined wire pin arrangement lines at different timings to reduce noise.
The serial impact printer for striking a recording paper with a wire pin array provided for a printing head is widely used because of its excellent cost performance. However, since a number of wire pins are collided against a recording paper at the same time, there exists a problem in that the printing noise is large. The methods of overcoming the above-mentioned problem are disclosed in Japanese Published Unexamined Patent Application No. 50-104534 and 56-144170. In the case of the Application No. 56-144170, as shown in FIGS. 1A and 1B, the wire pin arrangement line 62 or lines 64 of a printing heads 61 or 63 are arranged being inclined by an angle--with respect to a virtual vertical printing direction; and the wire pins are driven by drive pulses of different delay times generated by delay circuits 51 to 54 as shown in FIG. 2 to print character lines along the virtual vertical direction as shown in FIGS. 1C and 1D, with the result that a number of printing wires are not driven at the same time for reduction of noise.
In the above-mentioned prior art printing timing control method by use of the time delay circuits, however, since it is require to complete the driving operation of all the wire pins within a one printing period, in the case of a high speed printing it is difficult to obtain sufficient delay time, so that the wire pin driving time periods overlap with each other and thereby it is impossible to sufficiently reduce the printing noise. In addition, in case where the mounting angle .theta. of the inclined printing head deviates mechanically by an error .DELTA..theta. as shown in FIG. 3, it is difficult to achieve an accurate printing by simply determining a delay time corresponding to the mounting angle .theta..
Further, in the printing head of the prior art printer, the arrangement position of the wire pins is different from the ordinary wire pin arrangement position (i.e., the wire pins are arranged in the virtual vertical direction). This is because character patterns must be printed accurately even under the condition that the wire pin arrangement lines are inclined by a predetermined angle .theta.. In other words, since the prior art printing head is a special one, and therefore the ordinary printing head is not usable as the prior art printing head.